Patients in hospital intensive care units (ICUs) are physiologically fragile and unstable, generally have life-threatening conditions, and require close monitoring and rapid therapeutic interventions. They are connected to an array of equipment and monitors, and are carefully attended by the clinical staff. Staggering amounts of data are collected daily on each patient in an ICU: multi-channel waveform data sampled hundreds of times each second, vital sign time series updated each second or minute, alarms and alerts, lab results, imaging results, records of medication and fluid administration, staff notes and more. Petabytes of data are captured daily during care delivery in the country's ICUs; however, most of these data are not used to generate evidence or to discover new knowledge. The technology now exists to collect, archive and organize finely detailed ICU data, resulting in research resources of enormous potential. Since 2003, our group has been building the Multi-parameter Intelligent Monitoring in Intensive Care II (MIMIC II) Database, which now holds clinical data from about 40,000 entire stays in the ICUs of the Beth Israel Deaconess Medical Center (BIDMC) in Boston, including waveform data (continuous multi-channel recordings of physiologic signals and vital signs) for a subset of these stays. We have meticulously de-identified the data and freely shared them with the research community via the PhysioNet web site. The database is an unparalleled research resource and its value is widely recognized. More than 725 researchers have no-cost access to the clinical data under data use agreements (DUAs). This worldwide community includes academic, clinical, and industrial investigators from more than 32 countries and is growing by over 50% per year. In addition, thousands of investigators, educators, and students have used the waveform data, which we have made freely available to all without restriction. MIMIC II's demonstrated and substantial relevance for research can be enhanced by incorporation of new data, reflecting changes in patient populations, public health challenges, available medications, clinical interventions, and care guidelines, and by development of advanced software to facilitate user access to MIMIC II. Its value can be further enhanced by integration of data from multiple centers. This proposal seeks funding: a) to maintain, enhance, and document the open-source software that we have created to build and update MIMIC II, to incorporate established and emerging standards, and to provide the tools needed to create parallel data collections at other centers; b) to establish the first public, multi-center, international, scalable, continuously updatable, high-resolution data archive for critical care research; and c) to create new knowledge and to develop clinical tools, based on the data archive, to inform and support clinical decisions and practice in critical care.